Gas turbine nozzle



A HOWARD GAS TURBINE NOZZLE Filed April 25, 1944 June-19, 1945.

' Patented June'19, 1945 GAS TURBINE NOZZLE Alan Howard, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 26, 1944, Serial No. 532,784

Claims.

In connection with the design of gas turbines, the tendency is to utilize higher and higher temperatures. Temperatures of the order of 1500 F. are now commonly utilized and much higher temperatures are contemplated. The gases are generated by burning fuel and compressed air in a combustion chamber or a plurality of combustion chambers. From the combustlon chambers or chambers, the gases are supplied to an annular nozzle box from which they flow through the nozzle passages to the turbine wheel or wheels. The nozzle passages are formed from two relatively heavy rings between which are nozzle partitions which define the contour. of the" passages; ,the nozzle partitions are rigidly attached to-the two rings in any suitable manner, for example, by welding or by being initially cast integral therewith. Such nozzle partitions are curved, have rounded, relatively thick admission ends or entrance portions and taper to provide relatively'thin discharge ends or exit portions.

In the operation of a gas turbine, a uniform temperature does not obtain radially across the nozzle partitions, the partitions being hottest at their radially central portions and cooler at their radially outer and inner ends. This condition obtains due to one or more of several causes. Radiation of heat from the nozzle par-' titions is more rapid at their ends than at their central portions, and this condition may be magnified when special cooling means are provided for the nozzle partitions; an even temperature may not obtain throughout a combustion chamber with the result that the gases flowing from it to the nozzle box and thence through the nozzle,

some designs, this is because the edges are elongated permanently while hot which may tend to tear them. Then, when the nozzle partitions cool 01!, the long thin exit edges are pushed into an irregular bow during contraction. In other designs, the edges may be shortened while hot and there may be a tendency to tear the edge on cooling. In instances, the expansion due to unequal'temperature distribution has caused a pull on such edges sufilcient to cause them to crack.

The object of my invention is to provide an improved construction and arrangement for overcoming the above difficulty, and for a consideration of what I believe to be novel and my invention, attention is directed to the following specification and to the claims appended thereto.

In the drawing, Fig. 1 is a side view of a portion of a gas turbine embodying my; invention; Fig. 2 is a detail sectional view on a larger scale taken on line 2-2, Fig. 1 ,and Fig.3 is a detail sectional view taken on line 3-3, Fig. 2.

Referring to the drawing, l indicates the nozzle box of a gas turbine to which gases are supplied through a conduit 2, and 3 indicates the turbine wheel carried on a shaft 4 and provided with a ring of buckets 5. Gases are directed from the nozzle box to the turbine wheel by a nozzle ring comprising outer and inner-annular rings 6 and 1 between which are located the curved nozzle partitions 8 which define the nozzle passages 9. As shown particularly in Fig. 3, the nozzle partitions have rounded relatively thick inlet ends and relatively thin tapered exit ends. The foregoing construction is to be taken as typical of any gas turbine construction.

According to my invention, I provide a thin.

By a thin slot, I mean a slot having a width of the order of 10 to 20 mils. For example, but not by way of limitation, I have found in the case of a nozzle partition having a chord of 4 inches, a slot 0.5 inch long and 0.1 inch wide to be satisfactory. Preferably, I form each slot lll'approximately at the pitch line that is near the radial center of the nozzle partition for the reason that this gives the shortest non-slotted length of edge.

A central slot is preferableto two slots, one at each edge, because the central slot leaves the edge supported against vibration by the end walls, rather-than being out free.

I have found that by providing such a slot In in each nozzle at or near to the pitch line, I overcome the dimculties above pointed outxthe slot serving to provide suflicient space for expansion and contraction and serving to reduce the radial-strain setup in the nozzle edge such as would cause the formation of a crack.

My invention is of particular importance to nozzle partitions but in m ny instances it may ing partition or blade members with thin edge portions held between an inner ring or disk and an outer ring or shroud. Broadly, my invention applies to arrangements forming fluid passageways which have a partition or blade secured at r its ends between inner and outer rings or walls and having a cross section tapering into a relatively-thin edge portion. By providing an intermediate part of such edge portion with a transverse slot extending from the front to the back of the blade member the tendency of cracking or warping of the edge portion is materially reduced.

In accordance with the provisions of the patent statutes, I have described the principle 01' operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatu shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a gas turbine for operation at high temperatures, a nozzle structure comprising outer and inner rings between which are nozzle partitions united thereto and defining nozzle passages, said nozzle partitions having thin exit edges and each exit edge being provided with a transverse slot which extends from the exit edge upstream as regards the flow of gases through the nozzles.

2. In a gas. turbine for operation at high temperatures, a nozzle structure comprising outer and inner rings between which are nozzle partitions united thereto and defining nozzle passages, said nozzle partitions having thin exit edges and each exit edge. being provided at its pitch line 0 with a transverse slot which extends from the exit edge upstream as regard the flow of gases through the nozzles.

3. A nozzle partition for a gas turbine i'or operation at high temperatures having a thin exit 15 edge provided with a transverse slot which extends inwardly from such edge. 4. A nozzle partition for a gas turbine for operation at high temperatures having a thin exit edge provided at its pitch line with a transverse 20 slot which extends inwardly from such edge.

25 edge portion of a thickness decreasing toward its edge and a slot extending transversely'throughan intermediate part of such edge portion.

ALAN HOWARD. 

